A3 m long plank with a weight of 130 n is placed on a dock with 1 m of its length extended over the water. the plank is uniform in density so that the center of gravity of the plank is located at the center of the plank. the boy with the weight of 180 in the standings plank and moving out slowly from the edge of the dock.
how far from the pivot point at the edge of the dock is the center of the plank?
what is the torque exerted by the weight of the plank about the pivot point at the edge of the dock? (treat all the weight as acting through the center of gravity of the plank).
how far from the edge of the dock can the boy move until the plank is just on the verge of tipping? round to the nearest hundredths place.

In a thunderstorm, charge builds up on the water droplets or ice crystals in a cloud. thus, the charge can be considered to be distributed uniformly throughout the cloud. for the purposes of this problem, take the cloud to be a sphere of diameter 1.00 kilometer. the point of this problem is to estimate the maximum amount of charge that this cloud can contain, assuming that the charge builds up until the electric field at the surface of the cloud reaches the value at which the surrounding air breaks down. this breakdown means that the air becomes highly ionized, enabling it to conduct the charge from the cloud to the ground or another nearby cloud. the ionized air will then emit light due to the recombination of the electrons and atoms to form excited molecules that radiate light. in addition, the large current will heat up the air, resulting in its rapid expansion. these two phenomena account for the appearance of lightning and the sound of thunder. take the breakdown electric field of air to be eb=3.00ă—106n/c. part a estimate the total charge q on the cloud when the breakdown of the surrounding air is reached. express your answer numerically, to three significant figures, using ďµ0=8.85ă—10â’12c2/(nâ‹…m2) .

Can anybody me with this? ? (picture included.)

You throw a baseball directly upward at time =0 at an initial speed of 14.9 m/s. what is the maximum height the ball reaches above where it leaves your hand? ignore air resistance and take =9.80 m/s2.